Double skin sheet metal structural element



Jan. 1,5, 1946;. A. J. GRAFMAN DOUBLE SKIN SHEET'MTAL STRUCTURAL ELEMENT F-iled Nov. 18, l1940 2 Sheets-Sheet 1 IN1/5N TO Jan.15,1946, Y A.J.GRAFMAN 2,392,818

DOUBLE SKIN SHEET METAL STRUCTURAL ELEMENT Filed Nov. 18, 1940 2 Sheets-Sheet 2 Patented Jan. 15, 1946 .FFlcE DOUBLE SKIN SHEET METAL STRUCTURAL ELEMENT AbrahamJ'ack Grafinan, North Hollywood, Calif.,

assigner to Lockheed Burbank, Calif.

Aircraft Corporation,

Application November 18, '1940, Serial No. 366,095

1 claim; (o1. 18a-37) n This invention relates to an improved and simplied airplane wing rib, or other structural memsimple complementary sheet stampings, by means of spot or roll welding, riveting. or bolting in the case of metal, and cementing in the case of plastic.

It has heretofore been proposed to assemble wing ribs 4or the like from sheet metal in the form of channels or box sections, but such constructions used straight or uniform sections secured in overlapping or straddling relationship on the principle common to built-up structural beams and columns. Such lap joints add to the weight of theA structure, as well as the cost of manufacture and assembly of the resulting unit, as well as the individual struts and beams forming part of the final unit.

It is accordingly an object of this inventio-nl to provide an improved and-simplified sheet metal structural member for such parts as the ribs of airplanes, wherein a double skin or hollow section Ais formed from complementarystampings embodying the entire rib structure between longitudinal members suchas beams, the two complementary members being assembled along a median line by spot welding and riveting together .suitable flanges bounding apertures formed in the .n stresses without localized weak points or overlapping joints involving excess material and weight.

It is a further object of this inventionto form a rib or structural member o1' complementary 4ber, particularly adapted for fabrication from the parts in alignment during the spot welding operation. 1

vIt is alsov an object of this invention to provide an improved and simplied rib construction comprising stamped complementary halves so formed that the webs thereof will be arranged in spaced relationship by means of coacting ang'es, the webs being formed with beads and` contacting depressions to reduce or eliminate dat plate areas and thus reduce buckling tendencies, the remaining nat plate areas being reinforced if necessary by channel sections inserted between the webs and spot welded, bolted or riveted in place to make the i ,spaced webs work together rather than separately.

t in elevation." 1

sections which may be formed complete in single l operations and assembled along a median line, without the use of expensive jigs or the like, by riveting or otherwise temporarily or permanently fastening abutting flanges togetherat intervals, such as at changes in curvature ofthe anges, and thereafter spot welding together the intervening lengths of anges between rivet locations; the rivets or other clamping means serving to hold It is a further object of this invention to provide an improved and simplified structural element for ribs or the like wherein the spreading or flanging of the supporting surface of the rib adds to the end iixity of the stressed skin structure of the wing, thus allowing the use of higher compression stresses in the wing covering and supporting structure and stiening said supporting structure thus reducing buckling; and also providing resistance to crushing forces tending to produce deflections and consequent instability of the wing surface.

IOther and further important objects o1 this invention will be apparent from the disclosures in the specification and the accompanying drawings.

This invention is shown on the drawings as embodied in a rib section forming a transverse stiffenerfor a torsion box type of wing structure, it being understood the-invention is not limited to the embodiment chosen for illustrative purposes.

Figure I is a transverse section of a torsion box type of wing construction, including the nose section, but not the trailing edge section; a vrib embodying the features of this invention being shown Figure II is a fragmentary section on the line II-II of Figure I showing beaded and depressed areas used to break up large flat plate areas that would otherwise fail to carry 'stresses easily withsection of the wing.

r rthe rib with the-front shear beam.

Figure V is an enlarged fragmentary section on the line V-V of Figure Lshowing the stirrup supporting a longitudinal tension member of the wing, and an interiorly positioned channel adapted to supportl iiat plate areas of the rib webs to prevent buckling thereof.

Figure VI is a vertical section on the line Vif-VI, being in effect an end view of the center rib section with the rear shear beam web removed.

Figure VII is an enlarged section on the line VII-VII of Figure VI showing a reinforcement of the beam web nested in the end space or channel of the rib. v

, Referring to the showing on the drawings, the airplane wingsection as a whole comprises nose and center sections separated by a front shear beam Ill, a rear shear beam II completing a torsion box type of center section wherein upper and lower wing surfaces or skins I2 and I3 are respectively reinforced by a corrugated inner skin I4 struts 25, while the short beads or depressed areas spot welded back to back are suitable for other flat plate areas.

The nose section of the rib is similarly formed from complementary sheet metal webs 33 and 34 having lightening apertures 35 defining closed columns or struts 36, a continuous bead 31 being shown as stiliening both the struts and the' periphery or integral cap strip of the rib, which is iianged at 38 as before, and is joggled to receive the longitudinals I1, the flanges 38 bearing directly against the nose skin I6. Flat plate areas and Tvshaped longitudinals I5; the corrugations Hand upper skin I2 being-designed for compressive loading in a. cantilever wing, while the lower skin I3 and the longitudinals I5 are primarily designed for tension loads. The nose section comprises a formed skin I6 supported at intervals by hat section longitudinals I1, the margins of the skin I6 being attached to the forward anges of angle members I8 secured to the front shear beam, rear 'ilanges I8a of the web Ill supporting the center section skins I2 and I3, which are necessarily of heavier gage to transmit the main loads on the wing. The rear shear beam II is similarly' formed with angle "members I9 and flanges Illa on the web for attachment `of the skin I2 and I3, as well as the trailing edge skin 20 as indicated to the rear of the beam II. It is to be understood that ailerons, and aps, if the latter are used, are mounted adjacent to or on the rear shear beam II.

The center. section rib, between the two shear beams, comprises two complementary sheet metal web s 2I and 22 which can be formed or stamped out in single pieces and then assembled along their median line to produce a double web rib of the truss type, the diagonal stiieners of a built-up truss being approximated by providing lightening apertures 23 in the webs which apertures are bounded by flanges 24 lying in the median plane, the remaining web material between the apertures forming diagonal columns or struts 25 of hollow form having their axes intersecting near the upper and lower boundary or cap strips 26 and 21, these columns being longitudinally beaded as indicated at 23 to increase the stiffness thereof. The integral cap strips 26 and 21 formed by the spaced webs 2I and 22 approximate channels in form and the edges of the webs are turned out to form stiffening ilanges 28, the whole producing a iinal section resembling a hat section. It will be noted that the corrugated skin reinforcement I4 rests on the flanges 28 of the upper cap strip 26; while the tension longitudinals I5 are held in spaced relationship to the lower cap strip 21 by channel members 29 riveted or spot welded between the webs and serving to space and stiien the same against buckling.

Other hat plate areas in the webs can be stiffened by short beads, as at 30; by stamped depressions 3I, the -bottoms of which lie in the median plane and are spot welded together; or by inserting channel-like reinforcements 32 between the webs as indicated in Figure V. The reinforcing channel 32 is preferable at locations such as the inter-section of the axes of the columns or may be broken up as before, two spot welded depressions 3I being shown. n

The center and nose sections of the ribs have the opposed vertical edges of their spaced webs flanged outwardly as at 43 and 44 and secured through the we b of the front shear beam I0, as shown in Figure IV, the corners of the nose section being shown as further reinforced by flanged gusset plates 40, which may also be used on the center section if so desired. The rear end of the center rib section is shown in more detail in Figures VI and VII where the spaced webs 2I and 22 25 have out-turned flanges 4| and embrace a, hat section beam web stiffener 42, the iianges 43 o which are secured to the beam web II lby the rivets or fastenings for the rib anges 4I.

The complementary webs of the nose and cente;` sections of the rib are assembled together by spot welding and riveting the flanges 24 formed around the apertures 23, and are further tied together by the shear beams I0 and I I, depressions 3I and channels 32. Since the individual webs are formed by pressing over forms, or stamping 49 Spot welding, without clamps or holding xtures,

is facilitated by the use of roll welding electrodes for `straight lines or tangents, as well as open curves. Preliminary assembly is accomplished by rivets or other permanent or temporary 'fastenings applied at each end of the tangents and at several points in the nose circle, such rivets or fastenings aligning the complementary webs, and preventing distortion or relative slippage under the pressure of the spot welding tips or rolls.

It will be noted that three methods of longitudinal skin supporting structure have been disclosed in the center and nose sections, each having certain advantagesl while being generally interchangeable. For example, the corrugated inner skin I4 can be used for the nose or tension or lower side if desired and the nose construction shown herein could be used in the center section instead of the spaced rib iianges shown.

While the invention has been illustrated as applied to a rib for a relatively large airplane, it is evident that the principles of this invention are applicable to other structural elements such ,Y

formed with integral interior bracing, compris- 15 ing intersecting beaded columns having inturned marginal portions terminating in mating anges disposed in the median plane of the spaced web members, inserted reinforcing members positioned between the web members and rigidly secured thereto at an intersection of said columns to stitfen the at plate area formed by said intersection, means for permanently connecting said Web members along the edges of said mating flanges, and strips of channel form secured between the pairs of web members at intervals adjacent the lower edges thereof to serves as means to connect the web members to transverse members of the aerofoil.

ABRAHAM JACK GRAFMAN. 

